VacCirc-Vacuum Driven In-well Air Stripping and Recirculation

ABSTRACT

This invention has three parts: Part 1 Two-phase extraction of contaminated water and vapor from extraction wells using drop tubes with vertical slots or orifices; Part 2, Separation of extracted water and vapor/air at the wellhead or in a common manifold installed in ground, Part 3 injection of the extracted water using injection well with a drop tube similar to drop tube in the extraction well without the orifices or slots that extend above and below the water table. This invention strips volatile organic compounds from water, creates a recirculation cell in subsurface, increases biodegradation of organic compounds within the recirculation zone. This inventions also facilitate performing enhanced in-situ bioremediation or chemical oxidation by adding oxidation chemicals or bioremediation substance into the injection stream.

The invention relates to groundwater treatment by creating a recirculation system using extraction and injection wells, a vapor extraction and treatment system. Extraction of groundwater using a vacuum source and a drop tube is being used widely. This invention provides methods and apparatus to inject the extracted water back into the ground using gravity forces without a pump, or push mechanism. With this apparatus, a re-circulation cell is created to recapture injected groundwater by the extraction well, which is equipped with a drop tube extraction mechanism.

The product is comprised of the following components

Part 1—Groundwater extraction using a drop tube with vertical slots or holes extending from the bottom end of the tube below the water table to above the water table. The drop tube in the extraction well has vertical slots or holes in the bottom extending from below the water table to couple inches above the water table in the well that the tube is installed. When a vacuum is applied to the distal end of the tube, both water and air enter into the tube from the vertical slot or holes and both vapor and water are extracted together. During extraction over 90% of the volatile organic compounds (VOC) are stripped off from the water and transferred into vapor phase.

Part 2—This part includes separation of extracted water and vapor in above ground, in-ground or in-well separation column, and transferring the water using conveyance piping to injection well or injection zone in the same well separated by a packer from the extraction zone under vacuum tight condition.

Part 3—This part includes the injection of extracted groundwater using a drop tube without slots which is installed in an injection well or in the injection zone of the recirculation well.

Air and water will be extracted from the extraction well (or zone) using two-phase extraction with drop tube and vacuum. Volatile chemicals will be stripped off from the extracted water by the air during two-phase extraction in Part 1. The extracted water will be free of volatiles up to 99%. This cleaner water will be separated from the air/vapor in the separation column in Part 2. The water that is cleaner and separated from the air/vapor will be injected into the injection well/zone in Part 3.

Part 3 may also include injection of amendments for chemical oxidation or bioremediation into the drop tube under vacuum suction at the injection wellhead. This will allow performing in-situ chemical oxidation or enhanced bioremediation in the subsurface.

This invention may also be used to treat the contaminated water in above ground tanks.

This invention may be applied using two separate wells (one extraction and one injection well) installed in different boreholes (FIG. 1), one single well with two screen zones (one for extraction and one for injection, FIG. 2), A dual nested well pair installed in the same borehole with a dual completion separated by a bentonite seal with two screen intervals (not shown in figures).

FIG. 1 shows the invention with one extraction well (EW) and one injection well (IW). Referring to the FIG. 1, A is the well casing above the screen interval installed in a borehole drilled with a rig. The well casing is secured with bentonite or cement grout. B is slotted casing below the solid well casing (A) extending from total depth of the well to above the groundwater level. Fitter pack sand is used around the slotted casing interval (screen interval) of the well casing for both injection and extraction wells (not shown in figures). C is the capillary drop tube one-inch or smaller diameter extending from the total depth of the well to the top of the well casing. D is the vertical slots or holes in the bottom of the drop tube extending from the distal end of the drop tube to above the static groundwater level. E is the air and water separation column (or chamber). F is solid piping connecting the separation column (E) to the extraction blower for vapor flow. G is solid piping connecting the separation column (E) to the injection well for water flow. H is the drop tube without slots or holes in the Injection well. When vacuum is applied at F, the vacuum will be equally distributed to the separation column (E) and injection drop tubes (H) and extraction well drop tubes (C). Water in the extraction well and injection well will rise as a response to the vacuum. Air will enter to the drop tube in the extraction well from vertical slots (D) and lift the water to the separation column (E). Since there are no holes or slots in the drop tube (H) in the injection well, there will be no flow to the separation column from the injection well. Water in the separation column will drain into the injection well under gravity flow. During extraction and air entrainment in the drop tube in the extraction well, most of the volatile compounds will be stripped off from water and transferred into the vapor phase and treated in the vapor treatment system. Water with less volatile compounds will be recirculated from the injection well to the extraction well in the subsurface through the soil and groundwater zone.

FIG. 2 shows the invention with one well with dual screen zone configuration. A is the recirculation well (RW) is a polyvinyl chloride (PVC), 4-inch or larger diameter well. RW have two screen intervals: shallow screen interval (B) and deep screen interval (C). Both screen intervals are enveloped with filter pack sand (not shown in figures) to allow flow from the well to the surrounding soil. There is a blank casing between two screen intervals secured with bentonite seal (not shown in figures) in the annulus of the borehole between two filter pack sand (not shown in figures) intervals. A smaller diameter (2-inch diameter) inner well (D) is installed inside the larger diameter well. The inner well has a screen (slotted casing) in the deeper screen zone (C) of the larger diameter well. The inner well is secured in the larger diameter well with a packer (E) placed between inner well and larger diameter well, between shallow (B) and deep screen zone (C) of the larger diameter well. An extraction drop tube (F) is installed inside the inner well casing (D) extending from the bottom of the inner well casing to several feet above the inner well casing. The extraction drop tube (F) has holes or vertical slots from bottom of the drop tube to above the static water level. The extraction drop tube (F) is connected to the injection drop tube (I) above the inner well casing, inside the larger diameter well using an elbow and a tee (G). Injection drop tube extends from top of the packer to the top of the larger diameter well. After both drop tubes are installed the injection side need to be primed with addition of water above the packer and above the bottom end of the injection drop tube into the larger diameter well. A flapper valve can also be installed to the bottom of the injection drop tube to prevent air flow into the injection drop tube. When vacuum suction is applied to the injection drop tube above the larger diameter well, the vacuum will be transferred to both bottom end of the injection and extraction drop tubes. Water will rise in both drop tubes as a response to the vacuum. For example: If 10-inches of water vacuum is applied, water will rise 10-inch in both drop tubes. Since there are some holes or vertical screen extending above water level in the extraction drop tube, air will enter into the extraction drop tube and will lift the water and air to the elbow and tee connection (G) to the injection drop tube (I). Since no holes are installed in the injection drop tube, there will be no air entrainment or flow. Water from extraction tube will drop into the injection drop tube at the tee. Air and vapor from the extraction drop tube will move upward into the vacuum blower and to vapor treatment system. When the water column pressure in the injection drop tube is higher than the applied vacuum, water in the injection drop tube will flow out from the bottom into the larger diameter casing above the packer. Water will eventually rise to the shallow screen interval of the larger diameter well and flow out into the surrounding soil. Water, then will percolate downward in the soil to the deeper screen interval and create a recirculation zone. During extraction with air entrainment, volatile compounds will be removed from the water by air stripping, and dissolved oxygen in the water will be increased. This cleaner and oxygen rich water will strip off more contaminants from the soil as it is being recirculated. Extracted vapor will be treated by a surface vapor treatment system. If desired, in-situ chemical oxidation amendment may be added to the injection side of the recirculation well above the packer (H). Water with amendment will recirculate and react with the contaminant in the soil and groundwater.

FIG. 3 shows the wellhead air/water separation system for dual well operation of (two separate wells) vacuum driven in-well stripping and recirculation system. A is extraction well head that is equipped with a cap to secure two drop tubes to the 4-inch extraction well casing. B is extraction drop tube as shown in the FIG. 1 (C). C1 and C2 are 4 inch PVC tees installed on top of each other to create air/water separation column. This can be modified and replaced with a smaller diameter PVC tees or custom manufactured container or a tank. Extraction drop tube is connected to the upper tee (C1) as shown. Excess water recirculation drop tube (D, FIG. 1-I) is connected to the lower tee (C2) as shown. An elbow (E) was placed bottom of the tee (C2) and connected to the piping extending to injection well drop tube (G). Top of the upper tee (C1) is connected to the vapor extraction line (F). Injection drop tube (G) is secured on injection well head (H) and extends to the bottom of the Injection well as shown in FIG. 1 (H).

When Vacuum is applied to the vapor extraction line (F), the vacuum transferred to the extraction drop tube (B), excess water recirculation drop tube (D) and Injection drop tube (G). Bottom end of both Injection drop tube (G) and excess water recirculation drop tube (D) are submerged under water and have no holes or vertical slots above the water table. Extraction drop tube (B) has holes above the water level. When vacuum is exerted to drop tubes, water and vapor will flow from extraction drop tube (B) into the upper tee (C1) and water will be separated from vapor. Vapor will flow to the vapor extraction line (F) and treated by the vapor treatment system and discharged to the atmosphere. Water will flow down into the lower tee (C2) and elbow (E) under gravitational forces. Water will continue to flow to the injection well drop tube (G) and flow to the bottom of the drop tube and into the injection well screen. Water will create mound in the injection well as recirculation continues and will flow into the soil through the screen zone and the filter sand under gravitational forces. This water will be captured by the drawdown cone created by the extraction well, eventually creating a closed loop recirculation cell in the subsurface as shown in FIG. 1. When rate of extraction exceeds the rate of injection due to lower capacity of the injection well or lower permeability of the soil around the injection well, water will rise in the injection well. As a response to the rising water in the injection well, water in the injection drop tube will also rise and eventually may reach to the Elbow (E) and to the lower tee (C2). When the water rises to C2 location, the water will flow into the excess water recirculation drop tube (D) and flow back into the extraction well. This will reduce the rate of injection at the injection well by recirculating the excess water in the extraction well. This will allow injection to continue at a rate sustainable by the injection well. If necessary another injection well may be installed to receive some or all of the excess water. 

What is claimed is:
 1. Having a subsurface separation column that (1) accepts extracted water and vapor from upper section; (2) separates water and vapor; (3) diverts the water to the injection well from the bottom of the column; (4) diverts the vapor to the vacuum blower and to vapor treatment unit from the top of the column; and (5) have a water return line connected between injection water exit point and extraction water and vapor entry point. This extra line is designed to send extracted water back to the extraction well if injection well does not have enough capacity to accept all of the extracted water.
 2. Having an extraction well that is equipped with a drop tube (or capillary tube) that has vertical slots from couple inches above the water level in the well to the bottom of the drop tube.
 3. Having an injection well that is equipped with a drop tube without any slots and holes. The injection drop tube bottom end must be open and always submerged in water.
 4. having a single well recirculation cell that has: (1) a lager diameter well with two perforated zones separated by non-perforated zone; (2) a smaller diameter well inside the larger diameter well that extends between lower and upper perforated zones of the larger diameter well; (3) a packer around the smaller diameter well within the non perforated casing of the larger diameter well; (4) a drop tube placed into the smaller diameter well that extends to the bottom of the lower perforated zone of the larger diameter well; (5) a drop tube placed between the smaller diameter well and the larger diameter that extends to the top of the packer; (6) a connection between two drop tubes above the smaller diameter well and inside the larger diameter well, (7) an extension tube to extend the connected tube to surface for vapor extraction.
 5. Transferring extracted water to injection well by applying vacuum to both extraction and injection well and creating a recirculation zone in subsurface between extraction and injection well(s).
 6. Adding chemical oxidation or bioremediation substance to perform chemical oxidation or bioremediation using the suction in the drop tube at the injection wellhead. 